Like all companies, it varies with each exam. You can't beat AAMC for realism, but the revised Exams 1-5 from TBR are really good and show an excellent range from easy to difficult. The students I have known recently said that their instructors told them to take 1-5 as serious practice exams and use 6-whatever as good isolated practice, knowing there were too many hard passages and not enough easy ones in those tests.